Typical signal collection and processing systems detect the presence of signals of interest in an RF environment by determining whether signal power within a certain frequency range exceeds a predefined threshold level for a sufficient duration of time. "Channelized" systems, for example, tune a receiver having a known bandwidth to a certain frequency and collect all the RF energy present in the environment in that frequency range. These systems determine whether the signal power exceeds the predefined threshold and, if so, conclude that a pulse exists in that range. The channelizers then define a pulse start time as the time at which the signal energy first exceeded threshold, and a pulse end time as the time that signal energy falls below threshold. A known deficiency of such channelized systems is that they require significant resources to monitor a large number of frequency bands. Another deficiency of these systems is that each channelizer is tuned to a fixed bandwidth that may or may not be consistent with the bandwidths of the signals of interest. Consequently, these systems do not provide optimal sensitivity.
"Compressive receivers" continually sweep a broad bandwidth with a narrowband filter. These systems can detect narrowband pulses in a broadband environment, but suffer from an inability to detect the presence of signal energy that is present in the environment during periods in which the narrowband filter is not tuned to the frequency band in which that signal energy is present. Additionally, the bandwidth of the narrowband filter is tuned to a fixed bandwidth that may or may not be consistent with the bandwidths of the signals of interest. Consequently, these systems do not provide optimal sensitivity, do not necessarily capture the signal of interest, and are analog systems.
Instantaneous Frequency Measurement (IFM) receivers minimize the sweep time limitations of the compressive receiver by providing a broadband frequency discriminator that rapidly responds to a signal's presence. The IFM receiver, however, is unable to provide accurate frequency measurements in the presence of multiple simultaneous input pulses, as are typically encountered in crowded RF environments.
Broadband signal processing systems are often required to detect the presence of narrowband signal energy in a wideband RF environment that includes, for example, radar pulses and/or communications pulses. It is desirable that such systems are able to detect all that RF energy that is present in a wide frequency range for a certain period of time. It is also desirable to minimize the resources required to detect these signals. Designers of such signal processing systems, therefore, would benefit from methods and apparatus that analyze wideband radio frequency spectra that include both radar and communications signals to extract potential signals of interest while removing noise and other unwanted RF energy.